1. Field of the Invention
This invention is directed to a valve unloader assembly for a gas compressor, and more particularly to such an assembly in which a cylindrical valve guide cage or guard is movable relative to a concentrically positioned cylindrical valve seat or sleeve chair to place a plurality of poppet valves in the guide cage in an open position and therefore to unload the associated compressor.
2. Description of the Related Art
Gas compressors, such as those used in natural gas transportation pipelines and the like often use poppet valves for suction and discharge valves. In these and many other applications, poppet valves can provide reliable service as well as energy savings.
When conditions do not warrant full compression by the gas compressor, one or both ends of the compressor pistons must be "unloaded". This is usually done by bypassing the suction poppet valves so that gas is free to enter and leave the compressor cylinder from a suction chamber, thus allowing the compressor piston to idle back and forth under no load.
A number of prior art systems have been devised to selectively open or bypass similar valves in compressors or other fluid systems.
In U.S. Pat. No. 3,275,032 to Gruller, a plurality of "darts", each with an integral enlarged cam section, are selectively positionable to hold certain poppet valves open.
U.S. Pat. No. 3,455,335 to Pekarek teaches the use of a plurality of poppet valves in a fluid diverting valve, with each poppet valve having a stem which is selectively engaged by a movable actuator to open one or more of the valves.
U.S. Pat. No. 3,777,776 to Boisserand teaches a fluid distributor with a central bore surrounded by a plurality of cylindrical bores, each of which includes a sliding gate valve which is selectively operated via a pair of cam plates which move the valves within their respective bores.
U.S. Pat. No. 4,471,809 to Thomsen, et al. teaches a hydraulic control valve with a central cylinder with a number of orifices spaced thereabout and an outer, concentric cylinder with a like number of orifices. The cylinders are selectively rotatable relative to each other to align or misalign the orifices and thus open or close the valve. No poppet valves are used within the orifices.
Previous attempts to unload suction valves in gas compressors have included U.S. Pat. No. 4,043,710 to Bunn, et al., which is incorporated herein by reference, in which a compressor suction valve has a central passage therethrough. An unloading assembly includes a movable sleeve positioned within the central passage which selectively covers or uncovers ports which are positioned, when uncovered, to bypass a like number of poppet valves in the suction valve. In a similar system, U.S. Pat. No. 4,445,824 to Bunn et al. teaches a compressor suction valve clearance system in which a valve sleeve is movable relative to a tubular member within a compressor cylinder. An opening in the tubular member is selectively opened thereby to permit the compressor cylinder to communicate with a clearance pocket for unloading the compressor, or covered to allow the compressor cylinder to pressurize. Alternative manual and hydraulic operators are provided for moving the valve sleeve.
Such prior art unloading systems have utilized additional bypass openings in the compressor cylinder which must be closed for proper compressor operation. The provision of additional openings in the cylinder presents additional sealing problems. Furthermore, the slidable sleeves, although presenting a minimal surface area to the to the compressed gas within the cylinder, are still susceptible to buffeting and vibration from contact with the gas.
Accordingly, it is clear that a need exists for an improved system for unloading a suction valve in a compressor for a gas pressurization system. Such an unloading system should preferably not rely on additional bypass openings in the compressor cylinder, but, instead, should selectively hold the suction valves themselves open, thus eliminating the need for a valve bypass.